Failure to load bin clip shouldn't create a undo/redo
Scenario: a file is added to the bin, for example after recording from webcam. However, we assume that the file doesn't exists for some reason (eg: webcam capture failed).
What happens is that the clip will be created, and then the asynchronous loading will kick in but fail, silently supressing the clip from the bin. However, an undo object was created for the insertion of that clip. When one undoes then redoes, this insertion will happen again, creating an invalid disabled bin clip that cannot be deleted.
I guess a good approximation is to check whether the path is valid before creating the bin item.